What are the solutions of the equation x4 – 5x2 – 36 = 0? use factoring to solve.

X^4 - 5x^2 - 36 = 0
(x^2 - 9)(x^2 + 4) = 0  - factor the left side
(x + 3)(x - 3)(x^2 + 4) = 0 - factor (x^2 - 9 as difference of squares)
x + 3 = 0    x - 3 = 0    x^2 + 4 = 0  Set each factor to 0 if any 0 the left side 0
x = -3         x = 3         x^2 = -4
                                   x = 2i or -2i
The roots are 3, -3, 2i, -2i  (Don't know if you need the imaginary roots but I gave you them anyway)

The answer of the above is

Uneed to add them up 27+18+23=68